minimum spanning tree/shortest route problem

The Cebu Zoo Authority needs to identify the shortest path from Point 1 to Point 16 to reduce to reduce the travel distance that the zoo keeper has to walk (thereby increasing productivity) in order to open the exit gate of the zoo. The path must be consistent with the network shown.

1. what is the shortest path (define using the node numbers) through the network and how long is it?

2. if the route between nodes 7 and 10 should become blocked, i.e. remove the branch between nodes 7 and 10, what would be the next best alternative route(define using nodes) and the corresponding distance

3. if a new route were to be developed between nodes 5 and 9 w/ a length of 4 decimeters, what would be the shortest path through the network and its corresponding length? assume that nodes 7 and 10 are not blocked for this item.

4. would it be worthwhile to develop the new route between nodes 5 and 9 considering the following:

> cost to develop the new route is P75/decameter
> labor cost/meter traversed is P8/decameter

whew! this is no. 2 of my requirement. i answered no. 1 of course, but i need help on this. still a newbie in this field.
i do not require for you to answer them all items, but if you wish to, a million thanks to you!